Electric utilities and other providers of electric power have experienced many forms of tampering with conventional electric meters used to measure customer usage of electricity. One form of tampering is accomplished by applying large ferro-magnets to the outside of the meter housing. When this type of magnet is brought within close proximity of an electric meter, the magnetic fields generated by the magnet may interfere with the current sensors mounted within the meter cover. Consequently, the meter may be slowed down allowing the customer to cheat on the electric bill.
Conventional current sensors may also be susceptible to stray electromagnetic fields from other components within the meter housing. Accordingly, shields have been used in electric meters to attempt to protect current sensors from these stray electromagnetic fields. For example, U.S. Pat. No. 4,621,231 to Heinrich et al. and U.S. Pat. No. 5,223,790 to Baran et al. both disclose using conventional shields to protect current sensors from magnetic fields generated by other electrical components. U.S. Pat. No. 4,887,029 to Hemminger also discloses a device for shielding a current sensor from magnetic interferences generated by an adjacent current sensor.
In general, the conventional shields generally encapsulate the component, such as a current sensor, to be protected from magnetic fields. Consequently, these shields typically include multiple parts and are generally bulky. For example, in U.S. Pat. No. 4,413,230 to Miller, each transducer unit is completely surrounded by a shield including an inner and outer assembly. As a result, a significant amount of internal meter space is required to accommodate these shields. In addition, conventional shields may also lead to higher meter manufacturing costs and are not easily added to a meter in the late stages of meter assembly.
Electronic meters are generally smaller in size and have a lower profile than counterpart traditional electro-mechanical meters. Consequently, the smaller size of the newer electronic meters makes it difficult and impractical to use conventional encapsulating shielding. Moreover, improvements in current sensors may obviate the need for shielding from adjacent internal meter components; however, tampering from external magnetic fields is still a concern. Additionally, electronic meters may be easier and more cost effective to manufacture than traditional meters because assembly of the internal components of an electronic meter can be accomplished almost entirely by hand. The conventional encapsulating shields may not facilitate assembly by hand or the addition of shielding at a later stage in the meter assembly process for an electronic meter.